In internal combustion engines, camshafts are used for actuating the gas exchange valves. Camshafts are mounted in the internal combustion engine in such a way that cams attached to them bear against cam followers, for example bucket tappets, drag levers or rocker arms. When the camshaft is set in rotation, the cams roll on the cam followers which in turn actuate the gas exchange valves. Both the opening duration and amplitude but also the opening and closing time point of the gas exchange valves are defined by the position and shape of the cams.
Modern engine concepts tend toward a variable design of the valve drive. On the one hand, the valve stroke and valve opening duration are to be capable of being configured variably up to the complete cut-off of individual cylinders. For this purpose, concepts such as switchable cam followers, variable valve drives or electro-hydraulic or electric valve actuations are provided. Furthermore, it has proved advantageous to be able to exert influence on the opening and closing times for the gas exchange valves while the internal combustion engine is in operation. It is likewise desirable to be able to influence the opening and closing time points of the inlet and outlet valves separately so that, for example, a defined valve overlap can be set in a targeted manner. By the opening and closing time points of the gas exchange valves being set as a function of the current characteristic map range of the engine, for example of the current rotational speed or the current load, the specific fuel consumption can be lowered, the exhaust gas behavior can be positively influenced and the engine efficiency, maximum torque and maximum power can be increased.
The described variability in the gas exchange valve time control is brought about by means of a relative change in the phase position of the camshaft with respect to the crankshaft. Here, the camshaft is usually drive-connected to the crankshaft via a chain, belt or gearwheel mechanism or identically acting drive concepts. Between the chain, belt or gearwheel mechanism driven by the crankshaft and the camshaft is mounted a camshaft adjuster which transmits the torque from the crankshaft to the camshaft. Here, this device for varying the control times of the internal combustion engine is designed in such a way that, while the internal combustion engine is in operation, the phase position between the crankshaft and camshaft can be maintained reliably, and, if desired, the camshaft can be rotated within a certain angular range with respect to the crankshaft.
In internal combustion engines with a camshaft in each case for the inlet and the outlet valves, these may be equipped in each case with a camshaft adjuster. As a result, the opening and closing times of the inlet and outlet gas exchange valves can be displaced relative to one another in time and the valve time overlaps can be set in a targeted manner.
The seat of modern camshaft adjusters is generally located at the drive-side end of the camshaft. It is composed of a driving wheel which is fixed to the crankshaft, of a driven part which is fixed to the camshaft, and of an adjusting mechanism which transmits the torque from the driving wheel to the driven part. The driving wheel may be designed as a chain wheel, belt wheel or gearwheel and is connected fixedly in terms of rotation to the crankshaft by means of a chain, a belt or a gearwheel mechanism. The adjusting mechanism may be operated electromagnetically, hydraulically or pneumatically. It is likewise conceivable to attach the camshaft adjuster to an intermediate shaft or to mount it on a non-rotating component. In this case, the torque is transmitted to the camshafts via further drives.
Electrically operated camshaft adjusters are composed of a driving wheel which is drive-connected to the crankshaft of the internal combustion engine, of a driven part which is drive-connected to a camshaft of the internal combustion engine and of an adjusting mechanism. The adjusting mechanism is a three-shaft mechanism having three components which are rotatable with respect to one another. Here, the first component of the mechanism is connected fixedly in terms of rotation to the driving wheel and the second component is connected fixedly in terms of rotation to the driven part. The third component is designed, for example, as a toothed component, the rotational speed of which can be regulated via a shaft, for example by means of an electric motor or a braking device.
The torque is transmitted from the crankshaft to the first component and from there to the second component and consequently to the camshaft. This takes place either directly or with the third component being interposed.
By the rotational speed of the third component being suitably regulated, the first component can be rotated with respect to the second component, and consequently the phase position between the camshaft and crankshaft can be varied. Examples of three-shaft mechanisms of this type are inner eccentric mechanisms, double inner eccentric mechanisms, harmonic drives, swashplate mechanisms or the like.
To control the camshaft adjuster, sensors detect the characteristic data of the internal combustion engine such as for example the load state, the rotational speed and the angular positions of the camshaft and crankshaft. These data are fed to an electronic control unit which, after comparing the data with a characteristic map of the internal combustion engine, controls the adjusting motor of the camshaft adjuster.
DE 100 38 354 discloses a device for varying the control times of an internal combustion engine, in which the torque transmission from the crankshaft to the camshaft and the adjusting operation are implemented by means of a swashplate mechanism. The device consists substantially of a first bevel wheel which is fixed to the camshaft and has a first bevel wheel toothing, a second bevel wheel which is drive-connected to the crankshaft and has a second bevel wheel toothing, a swashplate and an adjusting shaft which is for example driven by an electric motor. The bevel wheels are arranged such that the bevel wheel toothings face one another in the axial direction. The swashplate which is mounted on the adjusting shaft is provided on its axial side faces with in each case one toothing and is arranged between the bevel wheels at a defined angle of incidence in such a way that the toothings of the swashplate engage in facing angular segments in the first and second bevel wheel toothing. Here, in the case of at least one of the toothed rim pairs, the toothings which engage into one another have different numbers of teeth.
A rotation of the adjusting shaft relative to the first or second bevel wheel leads to a wobbling rotation of the swashplate and consequently to a rotation of the engaged angular segments relative to the bevel wheels. On account of the different number of teeth of the toothings of a toothing pair, this leads to a relative rotation of the camshaft with respect to the crankshaft:
FIGS. 2 and 3 disclose a swashplate having a hub part and a toothing section which runs annularly around the hub part. The hub part is formed in one piece with the toothing section. An annular web extends outward in the radial direction from the hub part, which annular web runs out in a toothed section, with no teeth being formed in the region of the annular web. Furthermore, the teeth of the toothing section are of solid design, that is to say they extend in the axial direction from both axial side faces of the annular web.
On account of the solid design of the swashplate, said solution has the disadvantage of high rotating masses. Furthermore, the demand for axial installation space is relatively high.